In a typical cellular system, also referred to as a wireless communications network, wireless terminals, also known as mobile stations and/or User Equipment units (UEs) communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units within range of the base stations.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. In 3GPP this work regarding the 3G Long Term Evolution (LTE) system is ongoing.
A large variety of services have been developed for wireless communications networks to enrich user experience by exploiting the possibility of identifying user equipment coordinates in the network. The services can be private or public, commercial or non-commercial. Some examples of commercial services are navigation assistance, social networking, location-aware advertising, etc. Basic emergency services are typically provided publicly and a certain minimum coverage within the operator's network is often required by regulatory bodies.
User positioning, which means positioning of a user equipment used by a user, is the process of determining user equipment coordinates in space. User positioning in wireless networks is particularly interesting due to users' mobility, but is also challenging with wide-spread network coverage, various environments and the dynamic nature of radio signals. Once the coordinates are available, the position can then be mapped to a certain place, or location. The mapping function and delivering the location information on request are a part of the location service which is required for the basic emergency services. Services that further exploit the location knowledge or are based on it to offer customers some additional value are referred to as location-aware and location-based services, respectively.
Different user and network services require different positioning accuracy levels, which in turn depend, among the others, on the positioning method used. Below are some of the commonly known positioning methods used in wireless communications:                Cell Identification (CI) wherein serving cell coverage is associated with a certain area, which can be used together with timing advance, making positioning more precise by measuring the round trip time;        Triangulation based on estimating Angles Of Arrival (AOA) measured from the phase difference of signals received from the same user equipment by different antenna elements;        Trilateration based on estimating Time Of Arrival (TOA), wherein the distance is calculated by estimating TOA of received signals from three or more sites;        Multilateration based on estimating Time Difference Of Arrival (TDOA) of signals from three or more sites;        Assisted GPS (A-GPS) which combines the mobile technology and GPS and enhancing user equipment receiver sensitivity by providing orbit and other data to the user equipment.        
The accuracy of each of the methods depends also on the environment (e.g. rural, suburban, or urban; outdoor or indoor) and the measurements quality. A-GPS typically provides the best accuracy among the aforementioned methods, but requires GPS-equipped mobile terminals. TOA requires accurate time synchronization and in practice is less accurate than TDOA, although both methods require measurements from at least three sites.
Enhanced Observed Time Difference (E-OTD) and Observed TDOA (OTDOA), which are the two variants of TDOA, have been used in GSM and UMTS networks, respectively. Advanced Forward Link Trilateration (AFLT) has been adopted in CDMA networks.
Positioning procedure use any of the three approaches below:                Network-based, i.e. performed by the network (e.g., AOA),        Mobile-assisted, when a Serving Mobile Location Centre (SMLC) calculates the user equipment position based on the measurements reported by the user equipment (e.g., A-GPS, E-OTD, OTDOA), or        Mobile-based, i.e., performed by user equipment (e.g., CI, AFLT).        
A positioning method used in a cellular GSM network is depicted in U.S. Pat. No. 7,194,275 wherein additional control signals comprising virtual base station identification data are distributed in the radio system from well defined locations by e.g. transmitters. The control signals comprise base station identification data. The base station identification data is associated with a transmission location of the control signal comprising the base station identification data. Since there is a connection between each virtual base station identification data and the location from where it is transmitted, a mobile terminal can use the information for improving its position estimation according to conventional procedures. No modifications of the mobile terminals are therefore necessary. The mobile terminal is not able to connect to the communications system using the virtual base station identification data, since this data only is intended for position estimating purposes. In such a way, the devices for providing the additional information necessary for the improved position estimation can be made. However, in this method, a user equipment will spend unnecessary time and resources trying to establish whether the virtual cell is a good candidate for cell selection or reselection in idle mode, or handover in active mode. There is a also need to control or carefully plan the transmit power of the virtual base stations.
The positioning methods that will be used in LTE have not been specified yet.